High-severity wildfire reduces richness and alters the composition of
ectomycorrhizal fungi in low-severity adapted Ponderosa pine forests
Abstract
Soil fungal communities are vital for post-fire ecosystem restoration
because of their ability to cycle nutrients and form symbiotic
partnerships with regenerating trees. However, understanding is limited
about how high-severity wildfires influence the fungal community of
ecosystems adapted to low-severity fires. We studied an 11-year-old
chronosequence of high-severity burn ponderosa pine (Pinus ponderosa) in
eastern Washington, USA. Using Illumina MiSeq of the ITS1 rRNA, we
examined changes in soil geochemistry, and drivers of ectomycorrhizal
(EcM) and saprobic fungal richness, community shifts, and post-fire
fungal succession. High-severity wildfires reduced EcM fungal richness
by an average of 45.8% and saprobic richness by 11.7%, leading to
significant, long-term alterations to the post-fire fungal communities
that did not return to unburned levels even after 11 years. Over time,
differences in the post-fire fungal community were driven by the
dominance of several pyrophilous fungi, including the EcM Ascomycete
genera Pustularia and Wilcoxina, and the saprobic Basidiomycete genus
Geminibasidium, which decreased in abundance with time post-fire. EcM
fungi and saprobes were intimately linked to the soil environment: total
nitrogen, total carbon, and depth of organic matter predicted EcM
richness, while total carbon predicted saprobic species richness. We
conclude that high-severity wildfires reduced both EcM and saprobic
fungal richness and significantly altered the fungal community of this
fire-adapted ecosystem, selecting for resilient and fire-adapted
species, such as W. rehmii and Geminibasidium sp., thus initiating
post-fire succession.